Department of Entomology, Punjab Agricultural University, Ludhiana - 141 004, India.
*Part of the approved M.Sc. thesis submitted by the senior author to PAU, Ludhiana - 141004, India.
A direct relationship between sunshine exposure period and loss in original activity remaining (OAR) of foliar deposits of the HearNPV (PAU-1 Strain), when sprayed on the tomato (cv. Punjab Chhuhara) plants @ 109 occlusion bodies per ml, before sunrise, was observed by feeding periodically sampled foliar deposits to Helicoverpa armigera (Hübner) larvae (1.3±0.1 cm and 35±2.4 mg) in laboratory bioassay study. The LT50 varied between 132 and 264 hr at 4 and 132 hr sunshine exposures respectively, in contrast to 120 h only for unexposed virus (0 h). An initial loss of 5, 20 and 30 per cent in OAR intact was quite rapid at respective sunshine exposures of 4, 8 and 12 h only. Subsequent loss of 35 to 90 per cent in OAR intact was observed rather slowly within 24 to 156 h progressive exposures to the sunshine respectively. However, virus persisted on tomato foliage for 7 days with 10 percent OAR under Ludhiana conditions.
